Originally Posted by David Allaband
. . . Side note - This power plant doesn't idle. I'll begin the hunt for the culprit tomorrow. Start with fuel pump and carb.
Thanks a lot!
Do you mean that it runs under load, but stalls when the load is removed, or do you mean it fires up, and quits right away?
The old Onans had 3-wire control, hold start to common until it is running, hold stop to common until the last "chug" when you want to stop it. Once it develops oil pressure, an oil pressure switch activates a "run" relay that drops out the starter and keeps the ignition powered.
Controls on newer generators are 2-wire. Hold them together for as long as you want the generator to run, the engine stops when you release them.
I can't help you with the fourth wire, but with 3-wire control, there should be a spring loaded 3-position toggle switch with start and stop wires on the genset. You can duplicate the connection to this switch to remote push-buttons.
If the oil pressure switch is bad, the generator might start but will shut down when you release the "start" switch. And the starter will not stop turning until you do.
Some people try to make a 3-wire generator work on 2-wire control using an SPDT relay. The relay holds "start" forever when energized for a request-to-run, and holds "stop" forever when the run request is released.
A little-known fact I discovered is that if you have such a relay holding the "stop" button down, and you use the start switch on the generator, when there is no oil pressure the generator will ignore the "stop" and turn over the generator. As soon as there is pressure, the "run" relay controlled by the oil pressure will release the starter, look at the "stop" command and shut back down. It will do this start/stop for as long as both "buttons" are held down.
This may not be your problem, but I hope this helps you understand the older gensets. We had a professional Cummins/Onan mechanic condemn one of our old gensets because he "couldn't get the oil pressure relay to work." Years later when I discovered the start/stop issue, I'll bet he was being "Bit by the bear" trying the local start switch while a stop command was being held by the remote 2-wire to 3-wire relay in the control panel in the next room.